<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="generator" content="rustdoc">
<meta name="description" content="API documentation for the Rust `boxed` mod in crate `collections`.">
<meta name="keywords" content="rust, rustlang, rust-lang, boxed">
<title>collections::boxed - Rust</title>
<link rel="stylesheet" type="text/css" href="../../normalize.css">
<link rel="stylesheet" type="text/css" href="../../rustdoc.css">
<link rel="stylesheet" type="text/css" href="../../main.css">
<link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico">
</head>
<body class="rustdoc mod">
<!--[if lte IE 8]>
<div class="warning">
This old browser is unsupported and will most likely display funky
things.
</div>
<![endif]-->
<nav class="sidebar">
<a href='../../collections/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a>
<p class='location'>Module boxed</p><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#constants">Constants</a></li><li><a href="#traits">Traits</a></li></ul></div><p class='location'><a href='../index.html'>collections</a></p><script>window.sidebarCurrent = {name: 'boxed', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script>
</nav>
<nav class="sub">
<form class="search-form js-only">
<div class="search-container">
<input class="search-input" name="search"
autocomplete="off"
placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
type="search">
</div>
</form>
</nav>
<section id='main' class="content">
<h1 class='fqn'><span class='in-band'>Module <a href='../index.html'>collections</a>::<wbr><a class="mod" href=''>boxed</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>−</span>]
</a>
</span><a class='srclink' href='../../src/alloc/boxed.rs.html#11-752' title='goto source code'>[src]</a></span></h1>
<div class='docblock'><p>A pointer type for heap allocation.</p>
<p><code>Box<T></code>, casually referred to as a 'box', provides the simplest form of
heap allocation in Rust. Boxes provide ownership for this allocation, and
drop their contents when they go out of scope.</p>
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
<p>Creating a box:</p>
<pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="number">5</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0Alet%20x%20%3D%20Box%3A%3Anew(5)%3B%0A%7D">Run</a></pre>
<p>Creating a recursive data structure:</p>
<pre class="rust rust-example-rendered">
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">enum</span> <span class="ident">List</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Cons</span>(<span class="ident">T</span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">List</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>),
<span class="ident">Nil</span>,
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">list</span>: <span class="ident">List</span><span class="op"><</span><span class="ident">i32</span><span class="op">></span> <span class="op">=</span> <span class="ident">List</span>::<span class="ident">Cons</span>(<span class="number">1</span>, <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">List</span>::<span class="ident">Cons</span>(<span class="number">2</span>, <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">List</span>::<span class="ident">Nil</span>))));
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"{:?}"</span>, <span class="ident">list</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23%5Bderive(Debug)%5D%0Aenum%20List%3CT%3E%20%7B%0A%20%20%20%20Cons(T%2C%20Box%3CList%3CT%3E%3E)%2C%0A%20%20%20%20Nil%2C%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20list%3A%20List%3Ci32%3E%20%3D%20List%3A%3ACons(1%2C%20Box%3A%3Anew(List%3A%3ACons(2%2C%20Box%3A%3Anew(List%3A%3ANil))))%3B%0A%20%20%20%20println!(%22%7B%3A%3F%7D%22%2C%20list)%3B%0A%7D%0A">Run</a></pre>
<p>This will print <code>Cons(1, Cons(2, Nil))</code>.</p>
<p>Recursive structures must be boxed, because if the definition of <code>Cons</code>
looked like this:</p>
<pre class="rust rust-example-rendered">
<span class="ident">Cons</span>(<span class="ident">T</span>, <span class="ident">List</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0ACons(T%2C%20List%3CT%3E)%2C%0A%7D">Run</a></pre>
<p>It wouldn't work. This is because the size of a <code>List</code> depends on how many
elements are in the list, and so we don't know how much memory to allocate
for a <code>Cons</code>. By introducing a <code>Box</code>, which has a defined size, we know how
big <code>Cons</code> needs to be.</p>
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
<table>
<tr class=' module-item'>
<td><a class="struct" href="struct.Box.html"
title='struct collections::boxed::Box'>Box</a></td>
<td class='docblock-short'>
<p>A pointer type for heap allocation.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.ExchangeHeapSingleton.html"
title='struct collections::boxed::ExchangeHeapSingleton'>ExchangeHeapSingleton</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>This the singleton type used solely for <code>boxed::HEAP</code>.</p>
</td>
</tr>
<tr class='unstable module-item'>
<td><a class="struct" href="struct.IntermediateBox.html"
title='struct collections::boxed::IntermediateBox'>IntermediateBox</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p><code>IntermediateBox</code> represents uninitialized backing storage for <code>Box</code>.</p>
</td>
</tr></table><h2 id='constants' class='section-header'><a href="#constants">Constants</a></h2>
<table>
<tr class='unstable module-item'>
<td><a class="constant" href="constant.HEAP.html"
title='constant collections::boxed::HEAP'>HEAP</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p>A value that represents the heap. This is the default place that the <code>box</code>
keyword allocates into when no place is supplied.</p>
</td>
</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
<table>
<tr class='unstable module-item'>
<td><a class="trait" href="trait.FnBox.html"
title='trait collections::boxed::FnBox'>FnBox</a></td>
<td class='docblock-short'>
[<div class='stab unstable'>Experimental</div>] <p><code>FnBox</code> is a version of the <code>FnOnce</code> intended for use with boxed
closure objects. The idea is that where one would normally store a
<code>Box<FnOnce()></code> in a data structure, you should use
<code>Box<FnBox()></code>. The two traits behave essentially the same, except
that a <code>FnBox</code> closure can only be called if it is boxed. (Note
that <code>FnBox</code> may be deprecated in the future if <code>Box<FnOnce()></code>
closures become directly usable.)</p>
</td>
</tr></table></section>
<section id='search' class="content hidden"></section>
<section class="footer"></section>
<aside id="help" class="hidden">
<div>
<h1 class="hidden">Help</h1>
<div class="shortcuts">
<h2>Keyboard Shortcuts</h2>
<dl>
<dt>?</dt>
<dd>Show this help dialog</dd>
<dt>S</dt>
<dd>Focus the search field</dd>
<dt>⇤</dt>
<dd>Move up in search results</dd>
<dt>⇥</dt>
<dd>Move down in search results</dd>
<dt>⏎</dt>
<dd>Go to active search result</dd>
<dt>+</dt>
<dd>Collapse/expand all sections</dd>
</dl>
</div>
<div class="infos">
<h2>Search Tricks</h2>
<p>
Prefix searches with a type followed by a colon (e.g.
<code>fn:</code>) to restrict the search to a given type.
</p>
<p>
Accepted types are: <code>fn</code>, <code>mod</code>,
<code>struct</code>, <code>enum</code>,
<code>trait</code>, <code>type</code>, <code>macro</code>,
and <code>const</code>.
</p>
<p>
Search functions by type signature (e.g.
<code>vec -> usize</code> or <code>* -> vec</code>)
</p>
</div>
</div>
</aside>
<script>
window.rootPath = "../../";
window.currentCrate = "collections";
</script>
<script src="../../main.js"></script>
<script defer src="../../search-index.js"></script>
</body>
</html>
distrib
>
Mageia
>
6
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
564935689ab5527f955e5449ded02799
>
files
>
387
